The French town that hosted Pasteur’s silkworm-disease work beginning in 1865 was Alès. That year, chemist and government official Jean-Baptiste Dumas asked Pasteur to investigate pébrine, a devastating disease affecting silkworm farms in southern France and elsewhere in Europe.
Pasteur made several extended stays in Alès between 1865 and 1869, studying diseased silkworms, eggs, and chrysalises. Pébrine was associated with distinctive corpuscles visible under a microscope. Pasteur eventually developed a practical selection method: breeding stock was examined and material associated with disease was excluded, helping limit transmission.
His investigation was not straightforward. Pasteur initially confused pébrine with another silkworm disease, flacherie, and only gradually distinguished them. The episode nevertheless demonstrated how microscopy, controlled breeding, and attention to infectious agents could address an agricultural crisis. Alès is therefore the specific town associated with the beginning of this major phase of his research.